Christina Applegate's New Lease on Life

She has an "angel" of a boyfriend, Dutch bass player Martyn Lenoble, "who loves me from head to toe." She has a cozy Malibu beach house that she calls "the best thing I've ever done for myself." And, after a very public battle with breast cancer that has given her a gratifying "feeling of purpose," Christina Applegate has a new lease on life.

"I used to be really shy but I started to come into my own in my late 20s and early 30s," Applegate, 37, tells PEOPLE in the cover interview for the annual Most Beautiful issue. "Now I'm not afraid to speak up in a room full of people and be a part of the conversation."

The Samantha Who? star says she's finding balance and embracing her body after undergoing a double mastectomy in July, followed by reconstructive breast surgery in November.

"You have to get through the physical transformations then buck up, go to work and try to be the normal, happy Christina for everyone around you," she says.

One source of strength has been Lenoble. "He's been a friend for about 13 years," Applegate says. "Our relationship gets stronger and stronger. I'm really lucky."

And, more importantly, he makes the actress feel "beautiful" about her new body.

"I'm very grateful to Martyn for coming along at a time that he did because he's been my rock through all of this," Applegate says. "He gave me something to really want to live for and something to smile about."